High-intensity magnetic separator

ABSTRACT

A magnetic separator having a chassis, a rotor and a return roll supported on the chassis, the rotor and return roll having axes extending parallel to each other, and an endless band trained over the rotor and return roll, the endless band having an upper course and a lower course, the chassis being constituted by a beam positioned between the upper and lower course of the endless band. A frame supports opposite ends of the beam projecting from the opposite sides of the endless band at a plane of support, one of the beam ends being rigidly fixed on the frame, and a removable shim is positioned at the level of the lower course of the endless band adjacent the plane of support, the removable shim supporting the beam end opposite the one beam end on the frame whereby the beam is cantilevered on the frame when the shim is removed and a space is defined between the opposite beam end and the frame, the space permitting the endless band to be dismounted from, and mounted on, the rotor and return roll. Furthermore, a tensioning device applies an operating tension to the endless band mounted on the rotor and return roll, and may be deactivated to reduce the tension.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high-intensity magnetic separator forseparating products of low magnetic susceptibility, which comprises arotor consisting of a stack of pole pieces and disk-shaped permanentmagnets alternatingly disposed on a shaft, a return roll whose axis isparallel to that of the rotor, and an endless band trained over therotor and return roll under tension, the rotor and the return roll beingso positioned that the plane of the upper course of the endless band isapproximately horizontal. The rotor is coupled to a motor for rotatingthe rotor. In addition, such magnetic separators are equipped with adevice for applying an operating tension to the endless band to impartthereto sufficient traction to permit it to revolve without slippagewhen the rotor is rotated but so limited that the risk of tearing of theband is reduced.

2. Description of the Prior Art

In apparatus of this type, the endless band serves, on the one hand, toconvey the products to be sorted to the rotor and to remove theseparated magnetic particles, and on the other hand, to protect therotor against dirt and abrasion. The endless band is made of anon-magnetic sheet material of a small gage, of an order of magnitude of1/10th of a millimeter, so as not to affect the performance of the rotorappreciably. Because the endless band is so thin, it wears anddeteriorates rapidly and, therefore, it must be changed frequently.

To solve this problem, it has been suggested to provide a replaceableassembly comprised of the rotor and the return roll supported on achassis, so that a defective assembly may be replaced by an identicalone with a new endless band. The used band may then be replaced on theremoved assembly in a repair shop without causing an interruption of theoperation of the magnetic separator. This is expensive because itrequires two assemblies for a single separator.

SUUMARY OF THE INVENTION

It is the primary object of this invention to provide a magneticseparator in which a defective endless band may be rapidly, and withoutthe use of special tools, exchanged for a new band at the site ofoperation.

The above and other objects are accomplished according to the inventionwith a magnetic separator comprising a chassis, a rotor and a returnroll supported on the chassis, the rotor and return roll having axesextending parallel to each other, and an endless band trained over therotor and return roll, the endless band having an upper course and alower course. The chassis is constituted by a beam positioned betweenthe upper and lower course of the endless band, and a frame supportsopposite ends of the beam projecting from the opposite sides of theendless band at a plane of support. One of the beam ends is rigidlyfixed on the frame, and a removable shim is positioned at the level ofthe lower course of the endless band adjacent the plane of support, theremovable shim supporting the beam end opposite the one beam end on theframe whereby the beam is cantilevered on the frame when the shim isremoved and a space is defined between the opposite beam end and theframe, the space permitting the endless band to be dismounted from, andmounted on, the rotor and return roll. The separator further comprises atensioning device for applying an operating tension to the endless bandmounted on the rotor and return roll, and means for deactivating thetensioning device to reduce the tension.

According to a preferred feature of the present invention, the magneticseparator further comprises a counterweight disposed on an extension ofthe beam beyond the frame and arranged to balance at least partially thecombined weight of the beam, rotor and return roll when the beam is in acantilevered position. Advantageously, the counterweight comprises amotor means coupled to the rotor for rotating the same.

According to one embodiment, wherein the return roll has opposite shaftends displaceable in a direction extending approximately parallel to thecourses of the endless band, the tensioning device comprises springmeans biased against the opposite shaft ends, and the deactivating meanscomprises a movable abutment for the spring means, the movable abutmentbeing displaceable between an operating position, in which the springmeans is compressed and the endless band is tensioned, and a deactivatedposition, in which the spring means and the endless band are relaxed.The movable abutment may be a piston, and the tensioning device anddeactivating means further comprise a housing affixed to the chassis andhaving an axis extending approximately parallel to the courses of theendless band, the piston being arranged to glide in the housing, a rodextending from the piston through a slot in the housing and displaceablein the slot, the slot comprising two rectilinear portions extendingapproximately parallel to the housing axis, the two rectilinear portionsbeing of unequal length and being interconnected by a transverselyextending portion at ends of the rectilinear portions closest to thereturn roll whereby, when the rod is positioned at an end of the shorterrectilinear portion remote from the transversely extending portion, thespring means is compressed and, when the rod is at an end of the longerrectilinear portion remote from the transversely extending portion, thespring means is relaxed. Preferably, the rod has a sufficient length tobe able to be used by an operator for displacing the piston from theoperating to the deactivating position.

According to another embodiment, the tensioning device and means fordeactivating the tensioning device comprise two pneumatic jacks, acommon source of compressed air connected to the pneumatic jacks andadapted to apply equal pressure to opposite ends of the return rollwhereby the return roll tends to be moved away from the rotor, andreturn spring means adapted to move the return roll towards the rotorwhen the pneumatic jacks are disconnected from the common compressed airsource to relieve the pressure applied to the return roll ends.

The magnetic separator may further comprise means for applying to theendless band a pre-tension inferior to the operating tension bymodifying the distance between the return roll and the rotor when thetensioning device is deactivated.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, advantages and features of the presentinvention will become more apparent from the following detaileddescription of certain now preferred embodiments thereof, taken inconjunction with the accompanying somewhat schematic drawing wherein

FIG. 1 is a plan view showing the assembly of a rotor, a return roll andthe support chassis, without the endless band, of a high-intensitymagnetic separator, according to this invention;

FIG. 2 is an enlarged end view of the assembly of FIG. 1, partially insection, also showing the endless band;

FIGS. 3 and 4 are enlarged fragmentary views showing the tensioningdevice in the operating and deactivated positions, respectively;

FIG. 5 is a view similar to that of FIG. 2, illustrating anotherembodiment of the tensioning device;

FIG. 6 is a diagram showing the circuit for feeding compressed air tothe pneumatic jacks of the tensioning device of FIG. 5; and

FIG. 7 is a side elevational view of the magnetic separator of FIG. 1when the endless band is changed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawing and first to FIGS. 1, 2 and 7, there isshown a magnetic separator comprising chassis 10, rotor 12 and returnroll 14 supported on the chassis, the rotor and return roll having axesextending parallel to each other. The rotor is a magnetic rollconstituted by a stack of disk-shaped permanent magnets and pole pieces.Endless band 16 is trained over the rotor and return roll, the endlessband having an upper course and a lower course, and chassis 10 comprisesa beam positioned between the upper and lower course of endless band 16.This endless band serves to convey the products to be sorted to rotor12, the products being dumped on the band at inlet station A, themagnetic particles separated by the rotor being collected at B, and thenon-magnetic particles being discharged at C. At its opposite ends,rotor 12 has stub shafts mounted in bearings 18 affixed to chassis 10and it is rotated by a motor assembly 13 coupled to the rotor. Returnroll 14 is freely rotatably mounted on shaft 20 whose opposite ends mayglide in horizontal slideways 24 in two cheeks 22 of chassis 10. Thereturn roll has collars 23 at its opposite ends to assure centering ofendless band 16.

The support chassis for rotor 12 and return roll 14 is so conceived thatendless band 16 may be mounted thereon and removed therefrom simply bysliding it thereover. For this purpose, support frame 25 supportsopposite ends of the beam projecting from the opposite sides of endlessband 16 at a plane of support, the beam ends being affixed to frame 25by bolts 27. One of the beam ends, which is adjacent motor assembly 13,is rigidly fixed on frame 25, a bracket 31 (FIG. 7) being interposedbetween the support frame and the one beam end, and the one beam endbeing bolted to the bracket by bolt 27. A removable shim 29 (FIG. 2) ispositioned at the level of the lower course of endless band 16 adjacentthe plane of support, the removable shim supporting the beam endopposite the one beam end on frame 25, whereby the beam is cantileveredon the frame when the opposite beam end is unbolted and shim 29 isremoved. In this way, a space is defined between the opposite beam endand frame 25, the space permitting an operator to dismount the endlessband from, and mount it on, the rotor and return roll when the band isrelaxed, merely by sliding the band off the rotor and return roll, andthen in a reverse direction slipping a new band on the rotor and returnroll, as shown in FIG. 7. During this replacement operation, the beam iscantilevered on frame 25.

As shown in FIG. 7, motor assembly 13 is mounted on bracket 31 whichforms an extension of the beam beyond frame 25 and is arranged toconstitute a counterweight balancing at least partially the combinedweight of the beam, rotor and return roll when the beam is in acantilevered position. This reduces the mechanical stress on the boltsthat affix the chassis to the frame and on the frame itself. If desired,this balance may be further enhanced by providing a counterweight nextto the motor assembly, and in addition thereto, particularly in the caseof large-capacity magnetic separator with rotors of a large diameter.

The magnetic separator further comprises a tensioning device forapplying an operating tension to endless band 16 mounted on the rotorand return roll, i.e. a sufficient tension to enable the band to revolvewithout slippage, and means for deactivating the tensioning device toreduce the tension sufficiently to enable the endless band to be readilyremoved.

As shown in FIGS. 2-5, the opposite ends of shaft 20 bearing the returnroll are displaceable in a direction extending approximately parallel tothe courses of endless band 16, and in the embodiment illustrated inFIGS. 2-4, the tensioning device comprises coil spring 28 biased againstthe opposite shaft ends, and the deactivating means comprises movableabutment 30 for spring 28, the movable abutment being displaceablebetween an operating position, in which the spring is compressed and theendless band is tensioned, and a deactivated position, in which thespring and the endless band are relaxed. The illustrated movableabutment is a piston, and the tensioning device and deactivating meansfurther comprise fork-shaped bracket 26 articulated to each end of shaft20 and having a stem on which the piston is mounted, and housing 32affixed to cheeks 22 of the chassis and having an axis extendingapproximately parallel to the courses of the endless band, the pistonbeing arranged to glide in the housing. Rod 34 extends from piston 30through slot 36 in housing 32 and is displaceable in the slot, the slotcomprising two rectilinear portions extending approximately parallel tothe housing axis, the two rectilinear portions being of unequal lengthand being interconnected by a transversely extending curved portion atends of the rectilinear portions closest to the return roll (see FIGS. 3and 4) whereby, when rod 34 is positioned at an end of the shorterrectilinear portion remote from the transversely extending portion,spring 28 is compressed (FIG. 3) and, when the rod is at an end of thelonger rectilinear portion remote from the transversely extendingportion, the spring is relaxed FIG. 4). In the operating position,spring 28 is compressed between fork-shaped bracket 26 and piston 30 tomaintain endless band 16 tensioned, and in the deactivated position,return roll 14 is displaced towards rotor 12 to impart a slack to theband so that it may be replaced. The rod preferably has a sufficientlength to be able to be used by an operator for displacing the pistonfrom the operating to the deactivating position.

When piston 30 is in the operating position, coil spring 28 pushesreturn roll 14 away from rotor 12 with a sufficient force to permit theendless band to be revolved without slippage. The spring force is soselected that this force is low enough to avoid the risk of tearing theendless band. It may be regulated, for example, by interposing washersbetween spring 28 and bracket 26 and/or piston 30. Such an adjustmentmay be required if the length of the replacement band differs from thatof the removed band, for example.

In the embodiment illustrated in FIGS. 5 and 6, the tensioning deviceand means for deactivating the tensioning device comprise two pneumaticjacks 40 affixed to chassis 10, common source 44 of compressed airconnected to one chamber of the pneumatic jacks and adapted to applyequal pressure to opposite ends of return roll 14 whereby the returnroll tends to be moved away from rotor 12, and return spring 42 in theother chamber of the jacks adapted to move the return roll towards therotor when the pneumatic jacks are disconnected from the commoncompressed air source to relieve the pressure applied to the return rollends. The piston rods of the pneumatic jacks are articulated to theopposite ends of shaft 20 bearing return roll 14. As shown in FIG. 6,manually controllable valve 46 is interposed between compressed airsource 44 and pneumatic jacks 40.

In operation, sufficient compressed air is delivered to pneumatic jacks40 from compressed air source 44 to hold return roll 14 at a sufficientdistance from rotor 12 to keep endless band 16 under a uniform pressureover its entire width. When it is desired to replace the band, thedelivery of compressed air is cut off by valve 46, and the jack chambersconnected to compressed air source 44 are vented. Return springs 42 willthen cause the return roll to move closer to roll 12, endless band 16will be relaxed and the replacement operation can proceed in the mannerdescribed hereinabove in connection with the other embodiment of theinvention. Obvious, instead of using the illustrated pneumatic jackswith a return spring, double-acting pneumatic jacks may be used, i.e.counter-pressure may be produced by delivering compressed air to theother cylinder chamber instead of mounting a return spring therein.

If the tensioning device does not permit the dismounting of the endlessband, or makes the dismounting difficult, because the band is notsufficiently relaxed, as in the case, for example, in the magneticseparator disclosed in French patent No. 94 09617, the magneticseparator may further comprise means for applying to the endless band apre-tension inferior to the operating tension by modifying the distancebetween the return roll and the rotor when the tensioning device isdeactivated. For instance, the return roll may be mounted on the chassisas described above with reference to FIG. 2 and the pre-tensioning meansmay be constituted by fork-shaped elements articulated to the shaft ofthe return roll, each fork-shaped element comprising a screw-threadedpart carrying a nut bearing on an element of the chassis forming anabutment. By tightening or loosening the nut, one may change thedistance between the return roll and the rotor. The rotation of each nutmay be controlled by a friction clutch or a similar device to limit thepre-tension.

What is claimed is:
 1. A magnetic separator comprising(a) a chassis, (b)a magnetic rotor and a return roll supported on the chassis, the rotorconsisting of a stock of disk-shaped pole pieces and permanent magnets,and the rotor and return roll having axes extending parallel to eachother, (c) an endless band trained over the magnetic rotor and returnroll, the endless band having an upper course and a lower course, andthe endless band serving to convey products to be separated to themagnetic rotor and to remove magnetic particles separated by therotor,(1) the chassis being constituted by a beam positioned between theupper and lower course of the endless band, (d) a frame supportingopposite ends of the beam projecting from the opposite sides of theendless band at a plane of support,(1) one of the beam ends beingrigidly fixed on the frame, (e) a removable shim positioned at the levelof the lower course of the endless band adjacent the plane of support,the removable shim supporting the beam end opposite the one beam end onthe frame whereby the beam is cantilevered on the frame when the shim isremoved and a space is defined between the opposite beam end and theframe, the space permitting the endless band to be dismounted from, andmounted on, the rotor and return roll, (f) a tensioning device forapplying an operating tension to the endless band mounted on the rotorand return roll, and (g) means for deactivating the tensioning device toreduce the tension.
 2. The magnetic separator of claim 1, wherein thereturn roll has opposite shaft ends displaceable in a directionextending approximately parallel to the courses of the endless band, thetensioning device comprises spring means biased against the oppositeshaft ends, and the deactivating means comprises a movable abutment forthe spring means, the movable abutment being displaceable between anoperating position, in which the spring means is compressed and theendless band is tensioned, and a deactivated position, in which thespring means and the endless band are relaxed.
 3. The magnetic separatorof claim 2, wherein the movable abutment is a piston, and the tensioningdevice and deactivating means further comprise a housing affixed to thechassis and having an axis extending approximately parallel to thecourses of the endless band, the piston being arranged to glide in thehousing, a rod extending from the piston through a slot in the housingand displaceable in the slot, the slot comprising two rectilinearportions extending approximately parallel to the housing axis, the tworectilinear portions being of unequal length and being interconnected bya transversely extending portion at ends of the rectilinear portionsclosest to the return roll whereby, when the rod is positioned at an endof the shorter rectilinear portion remote from the transverselyextending portion, the spring means is compressed and, when the rod isat an end of the longer rectilinear portion remote from the transverselyextending portion, the spring means is relaxed.
 4. The magneticseparator of claim 3, wherein the rod has a sufficient length to be ableto be used by an operator for displacing the piston from the operatingto the deactivating position.
 5. The magnetic separator of claim 1,wherein the tensioning device and means for deactivating the tensioningdevice comprise two pneumatic jacks, a common source of compressed airconnected to the pneumatic jacks and adapted to apply equal pressure toopposite ends of the return roll whereby the return roll tends to bemoved away from the rotor, and return spring means adapted to move thereturn roll towards the rotor when the pneumatic jacks are disconnectedfrom the common compressed air source to relieve the pressure applied tothe return roll ends.
 6. The magnetic separator of claim 1, furthercomprising means for applying to the endless band a pre-tension inferiorto the operating tension by modifying the distance between the returnroll and the rotor when the tensioning device is deactivated.
 7. Themagnetic separator of claim 1, further comprising a counterweightdisposed on an extension of the beam beyond the frame and arranged tobalance at least partially the combined weight of the beam, rotor andreturn roll when the beam is in a cantilevered position.
 8. The magneticseparator of claim 7, wherein the counterweight comprises a motor meanscoupled to the rotor for rotating the same.